.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
.\" Portions extracted from linux/kernel/ioport.c (no copyright notice).
.\"
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.\" Modified Tue Aug  1 16:47    1995 by Jochen Karrer
.\"                              <cip307@cip.physik.uni-wuerzburg.de>
.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified Fri Nov 27 14:50:36 CET 1998 by Andries Brouwer <aeb@cwi.nl>
.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\"     Added notes on capability requirements
.\"
.TH IOPL 2 2016-03-15 "Linux" "Linux Programmer's Manual"
.SH NAME
iopl \- change I/O privilege level
.SH SYNOPSIS
.B #include <sys/io.h>
.sp
.BI "int iopl(int " level );
.SH DESCRIPTION
.BR iopl ()
changes the I/O privilege level of the calling process,
as specified by the two least significant bits in
.IR level .

This call is necessary to allow 8514-compatible X servers to run under
Linux.
Since these X servers require access to all 65536 I/O ports, the
.BR ioperm (2)
call is not sufficient.

In addition to granting unrestricted I/O port access, running at a higher
I/O privilege level also allows the process to disable interrupts.
This will probably crash the system, and is not recommended.

Permissions are not inherited by the child process created by
.BR fork (2)
and are not preserved across
.BR execve (2)
(but see NOTES).

The I/O privilege level for a normal process is 0.

This call is mostly for the i386 architecture.
On many other architectures it does not exist or will always
return an error.
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EINVAL
.I level
is greater than 3.
.TP
.B ENOSYS
This call is unimplemented.
.TP
.B EPERM
The calling process has insufficient privilege to call
.BR iopl ();
the
.B CAP_SYS_RAWIO
capability is required to raise the I/O privilege level
above its current value.
.SH CONFORMING TO
.BR iopl ()
is Linux-specific and should not be used in programs that are
intended to be portable.
.SH NOTES
.\" Libc5 treats it as a system call and has a prototype in
.\" .IR <unistd.h> .
.\" Glibc1 does not have a prototype.
Glibc2 has a prototype both in
.I <sys/io.h>
and in
.IR <sys/perm.h> .
Avoid the latter, it is available on i386 only.

Prior to Linux 3.7,
on some architectures (such as i386), permissions
.I were
inherited by the child produced by
.BR fork (2)
and were preserved across
.BR execve (2).
This behavior was inadvertently changed in Linux 3.7,
and won't be reinstated.
.SH SEE ALSO
.BR ioperm (2),
.BR outb (2),
.BR capabilities (7)
